Titanium-base alloys



Patented May 13, 1 952 TITANIUM-BASE ALLOYS Robert I. Jafiee, Horace R. Ogden, and Daniel J. Maykuth, Columbus, Ohio, assignors, by mesne assignments, to Remington Arms Company, Inc., Bridgeport, Cnn., a corporation of Delaware No Drawing. Application February 7, 1951, Serial No. 209,902

4 Claims. 1

cost, and it becomes desirable to alloy titanium with such other metals as will increase the strength to acceptable levels and preferably at the same time effect some reduction in the total material cost. Aluminum is a metal well suited to the attainment of these objectives, being low in weight, relatively low cost, and having a material strengthening effect on titanium. However, the amount of aluminum alone that can be added to titanium is limited by its adverse effect. on ductility. Binary alloys of titanium with more than about 5% of aluminum are too brittle for most structural uses; and such binary alloys containing less than about 5% of aluminum do not possess sufficient strength to be of general utility. A further strengthening, as well as an increase in the content of relatively inexpensive aluminum, is highly desirable.

The present invention comprises the discovery that the addition to titanium-aluminum alloys of a few percent of indium effects a marked improvement in the properties of titanium-aluminum alloys of a given aluminum content, say 3.5% to 5%, and likewise enables an increase of i the aluminum content to not less than 7.5%,

with a material increase in strength, while maintaining adequate ductility.

The metal used as a base for the alloys of the present invention may contain the interstitial contaminants, carbon, oxygen and/or nitrogen, up to at least the total quantity to be found in good quality commercial titanium. Carbon, for example, has been found to be beneficial when present in amounts between 0.02% and 0.3%, the latter being about the maximum amount which is soluble in alpha titanium. An excess of carbon tends to form embrittllng carbides. For a typical alloy, a carbon content of 0.1% to 0.2% is desirable, but the optimum amount varies with other factors. Nitrogen is a potent hardener of titanium but tends to cause embrittlement. The effect of the three contaminants being additive at a given strength level, the quantity of each which can be tolerated depends to a considerable extent upon the quantity of the others. The limiting factor is usually ductility, and the requirement as to ductility varies with the intended use of the alloy. Further, increasing the amounts of the substitutional metallic alloying ingredients tends to decrease the tolerance for the interstitial components, particularly embrittling nitrogen.

The alloys of this invention may be prepared by melt-casting in an atmosphere of argon, rolling at a suitable temperature, say 980 0., and annealing under conditions which will efiect recrystallization, but not substantial grain growth or re-solution of carbides. A typical but by no means universal'annealing treatment comprises soaking at a temperature of about 850 C. for about 3 hours. The rate of cooling after annealing is not material, since in these alloys the titanium is all in the alpha phase except for minor amounts which may be combined as; titanium carbide. The properties of selected alloys of titanium of requisite purity with aluminum and indium, as annealed for 3 /2 hours at 850 C., unless otherwise noted, appear in the table below, in which table bend ductility is measured as the radius upon which the alloy can be bent without fracture to an angle of the radius being stated as a multiple of the specimen thickness.

Microscopic examination shows most of the alloys of the present invention to be of small grain size, probably due to a fine distribution of carbides. Carbon is less soluble in beta titanium than in alpha titanium, hence in a melt containing, say 0.2 carbon, a substantial proportion of the carbon will be present as carbides, which as the melt congcals are frozen in a matrix of beta titanium in a fine dispersion. As recrystallization proceeds without substantial solution of carbides, the numerous carbide particles form nucleation sites for the growth of relatively small alpha grains, and inhibit the growth of large grains. Grain sizes as small as 0.012 mm. and 0.015 mm. have been observed repeated- 13;, and the average grain size --is from about 0.020 mm. to 0.030 mm. fine grain size, and the presence of visible carbide particle stringers are associated with the substantial diiierences between yield strength and ultimate strength appearing in the following table. This character- 3 istic renders the alloys universally useful, being particularly advantageous for sheet and other forms which are stretched in fabrication.

Typical alloys and their properties are as follows:

4 1% to about 5% indium, from about 0.02% to about 0.3 carbon, balance titanium.

2. An alloy consisting essentially of from about 3.5% to about aluminum, from about 1% to about 5% indium, from about 0.02% to Composition, (Balance Tltamum) Vickers 0.2% Offset Ultimate Bond Duc- Hardness p. s. i. p. s. i. tility T A] In C 5 1 321 82.000 94,000 0. 7 5 2. 5 326 90. 000 100,000 17 1. 5 5 5 320 80, 000' 93, 000 14 2. 2 7. 5 2. 5 S ll. )9, 000 101, 000 12 2. 2 10 2. 5 346 112, 090 114, 000 5 2. 1 5 2. 5 399 146', 000 154, 000 12 1. 3 7. 5 2. 5 383 124-, 000 126,000 -11 6. 1

l Annealed at 950 C.

The excellent strength and ductility of any of the foregoing alloys together with their stability upon exposure to temperatures at. least as high as 400 C., render them highly desirable materials for any uses requiring high ratio of strength-to-Weight, either With or Without exposure to high temperatures. They are especially valuable in the field of high speed aircraft and airborne equipment,

This application is a continuation-impart of application Serial No. 151,314, filed March 22, 1950', which is now abandoned.

What is claimed is:

1. An alloy consisting essentially of from about 3.5% to about 10% aluminum, from about 7.5% aluminum, 2.5% indium, 0.02% to 0.3%-

oarbon, balance titanium.

ROBERT I. JAFFEE; HORACE R. OGDEN. DANIELJ. MAYKUTH.

No references cited. 

1. AN ALLOY CONSISTING ESSENTIALLY OF FROM ABOUT 3.5% TO ABOUT 10% ALUMINYM, FROM ABOUT 1% TO ABOUT 5% INDIUM, FROM ABOUT 0.02% TO ABOUT 0.3% CARBON, BALANCE TITANIUM. 